The shooting star filler is on the foil Urza's Destiny sheet and is probably on the Urza's Legacy sheet as well. The shooting star filler is not a test print card it's just a normal filler from the foil sheet.

When did the filler 10 come about? If it wasn't before the Exodus test prints it probably wasn't created to test the foil star. In fact, the non-foil Exodus test prints are very likely the ones on which the star was tested, not the filler.

Then I guess it's possible, although Exodus was released in 1998, and if I am not mistaken test prints are created a couple years before a set's release. I still believe that the nonfoil Exodus test prints were created to test the foil star, as there honestly is no other reason why they would exist. The filler 10 material could conceivably have been a rough material test before they used the nonfoil test prints to test how the star would look if it was created early enough.